Apparatus and method of detecting the presence of flame in a
combustion chamber



y 1, 1966 w. L. LIVINGSTON 3, 7

APPARATUS AND METHOD OF DETECTING THE PRESENCE OF FLAME IN A COMBUSTION CHAMBER Filed July 15, 1964 /& U 42 sa Wm mull! FIG. 5

INVENTOR WILLIAM L. LNINGSTON AGENT United States Patent 3,253,579 APPARATUS AND METHOD OF DETECTING THE PRESENCE OF FLAME IN A COMBUSTION CHAMBER William L. Livingston, Minneapolis, Minn., assignor to Combustion Engineering, Inc., Windsor, Conm, a corporation of Delaware Filed July 13, 1964, Ser. No. 382,031

7 Claims. (Cl. 122-504) This invention relates to flame sensing and indicating apparatus and method as employed in connection with a combustion chamber. More specifically, the invention is concerned with an improvement in the apparatus and method for sensing and reporting black-out or loss of flame in the combustion chamber of a steam generator.

In the operation of a steam generator it is essential for maximum security and safety that the operator be reliably informed at all times and as speedily as possible of the presence or absence of flame in the furnace. Such knowledge will enable him to take the necessary steps in preventing a possible explosion that may be caused by the ignition of unburned fuel and air accumulated in the furnace chamber.

One well-known apparatus and method of sensing flameout in the furnace is based on the so-called pressure differential principle. A practical application of this principle is described in the United States Patent No. 3,123,027 issued on March 3, 1964, to William L. Livingston and entitled Apparatus and Method of Flame or Combustion Rate Detection in a Combustion Chamber.

A primary concern in designing flame detecting apparatus is the reduction or elimination of extraneous influences which may affect the clarity or retard the delivery of the flame sensing signal. One of these influence-s is i the stack effect caused by the column of hot gases or hot air which may be present in a furnace even though the actual flame or fireball has been extinguished or has not as yet been ignited.

It is accordingly a primary object of the invention to greatly reduce or eliminate the influence which the stack effect in the furnace, other than that caused by the flame itself, may have on the determination of a flame-on or flame-off condition in the furnace.

Other objects and advantages of the invention will become apparent from the following description of an illustrative embodiment thereof when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic representation of a steam generator equipped with the inventive flow detecting apparatus herein disclosed;

FIG. 2 is a simplified diagram similar to FIG. 1, but with the pressure taps of the flame detecting apparatus being arranged in a different manner;

FIG. 3 shows an apparatus for hydraulically balancing the pressure differential readings so as to compensate for different pressure tap spacings in the furnace wall;

FIG. 4 shows a diagram for electrically balancing the pressure difference readings, so as to compensate for different pressure tap spacings in the furnace wallgand FIG. 5 is an enlarged representation of the flame-on, flame-off indicating scale.

Referring now to the drawings wherein like reference characters are used throughout to designate like elements, the illustrative and preferred embodiment of the invention as depicted in FIG. 1 includes a steam generator designated generally as 10, having a furnace chamber 12 lined with water carrying and steam generating tubes 14. These tubes are supplied with feedwater from a steam and water drum 16 by way of downtake tubes 18 and.

header 20. The steam produced in furnace tubes 14 flows into drum 16 by way of tubes 22 and is delivered via tubes 24 to superheater 26, before turbine, not shown.

Fuel and air in controlled quantities are delivered to the furnace chamber 12 by way of air ducts 28 and fuel pipes 30, respectively, and are discharged thereinto through burners 32 for burning of the fuel. A body of flame or fireball is formed with the combustion gases rising in the chamber, imparting heat to the furnace tubes 14 and superheater 26, and egressing through a horizontal gas pass or offtake 34. Additional heating surfaces, not shown, may be passed over by the hot combustion gases before they are discharged to the atmosphere by Way of a stack, not shown.

The interior of an upright furnace chamber of the type herein considered can be divided into three heating zones with respect to the intensity of combustion taking place during operation thereof. An intermediate zone H wherein a high degree of heat is generated. This zone usually is situated opposite and slightly above burners 32. A moderate heating zone L located below the burners 32 and high heat zone H, and another moderate heat zone U located above the burners 32 and high heat zone H.

In accordance with the invention at least three pressure tap openings are provided in the furnace wall, a lower opening 36, an intermediate opening 38 and an upper opening 40. The space or distance d1 between open ings 36 and 38 generally encompasses the high heat producing zone H and the space or distance d2 between openings 38 and 40 lies in the upper moderate heat zone U. Pressure taps 36 and 38 are connected to a differential pressure indicating device 42 by means of conduits 41 and 43, respectively, and pressure taps 38 and 40 are connected to a differential pressure indicating device 44 by means of conduits 4S and 47, respectively. Devices 42 and 44 each comprise two pressure chambers 42a, 42b and 44a, 441), respectively. These two chambers are separated by di-aphragms 48 and 50, respectively. Attached to diaphragms 48 and 50 there are rods 51 and 52, respectively, which transmit the differential movement of the diaphragms to a balancing device generally designated 54. This device comprises a beam pivoted at 55 and having arms a1 and :12, with arms a1 connected to diaphragm 48 and arm a2 connected to diaphragm 50.

passing to a steam In accordance with the invention the ratio of arm length al to arm length a2 is inversely proportional to the ratio of distance d1 to distance d2. With other variables being equal, the stack effect as indicated by devices 42 and 44 is proportional to the distance between pressure taps 36 and 38 and the distance between pressure taps 38 and 40, respectively. Accordingly, by applying correction factors in inverse proportion to these distances, such as arms a1 and a2, the stack effect is thereby cancelled out in a furnace with no flame present.

On the other hand if a flame is in evidence, then the increased volume of the gases in space H between pressure taps 36 and 38 will immediately produce a pressure difference which is considerably larger than that produced in the space U, between pressure taps 38 and 40. Accordingly indicator 58 of instrument 54 will swing to the left thereby positively indicating that a flame has been established in the furnace. By the same token a return of the indicator 58 to the zero position would then definitely establish the fact that the flame has gone out and thereby initiate proper remedial action by the operator or by the automatic control system.

In FIG. 2 an arrangement is shown in which the lower moderator heat input zone L is straddled by two pressure tap openings 60 and 62, and the high heat input zone H is straddled by pressure tap openings 60 and 64. The lower pair of pressure taps 60 and 64 is connected to a pressure difference measuring instrument 66 and the upper pair 60 and 64 to a pressure difference indicating instrument 68, similar to the instruments 42 and 44 of FIG. 1. Each of instruments 66 and 68, respectively, has an upper space 66a and 68a in communication with pressure taps 60 and 64, and a lower space 66b and 68b in communication with pressure taps 62 and 60. A diaphragm 67 separating space 66a from space 66b is connected to a long lever arm a4, and a diaphragm 69 is connected to a short lever arm a3, with arms a3 and a4 constituting a beam pivoting about a support point 70. As in the embodiment shown in FIG. 1, the ratio of the arm lengths a3 to a4 is inversely proportional to the ratio of distances d3 to d4. Distance d4 traverses the space H in the furnace, the space which will produce the highest heat release when a flame is established in the combustion chamber 12.

Accordingly, in a cold or hot furnace with no flame present the stack effect will be cancelled out and indicator 58 will point to zero. However, as soon as a flame is established in space H the pressure difference across pressure taps 60 and 64 will increase at a greater rate over that across pressure taps 62 and 60, thereby swinging indicator 58 to the left. A flame out will immediately be evident by a return of the indicator 58 to the zero position.

While in FIGS. 1 and 2 correction of the stack effect is accomplished by balancing instrument 54, FIG. 3 illustrates a hydraulic means whereby the same result can be accomplished. Two pistons 71 and 72 supported on a common shaft 73, each divides corresponding cylinders 74 and 75 into spaces 74a, 74b and 75a, 75b, respectively. When applied to pressure tap locations as shown in FIG. 1, spaces 74a and 74b are in communication with pressure taps 40 and 38, respectively, and spaces 75a and 75b are in communication with pressure taps 38 and 36, respectively. In accordance with the invention the ratio of the area of piston 71 to that of piston 72 is inversely proportional to the ratio of distance d2 to distance d1. Accordingly, position of piston 71 would be indicative of the pressure difference between the pressure at points 38 and 40, and the position of piston 72 would be indicative of the pressure difference between the pressure at points 36 and 38, if both pistons were supported on separate shafts. However, since pistons 71 and 72 are carried on a common shaft 73 the position of pistons 71 and 72 or indicator 76 will point to zero when no flame is present and will move to the rightor positive side against a bias represented by spring 77, when a flame is present in space H of the furnace chamber.

When applying the hydraulic balancing device illustrated in FIG. 3 to the pressure tap locations shown in FIG. 2, spaces 74a and 74b will be in communication with pressure taps 62 and 60, respectively, and spaces 75b and 75a will be in communication with pressure taps 64 and 60, respectively.

In FIG. 4 a device is illustrated which balances by electrical means the difference between the pressures in the furnace at points 38, 40 and that between the pressures at points 36, 38. This device comprises a Wheatstonebridge circuit receiving AC. or DC. power across points B and D and indicating the bridgeoutput across points A and C such as by voltage meter 78. Two opposing arms A-B and DC of the Wheatstone bridge are provided with variable resistances Sand R, respectively. These resistances can be in the form of strain gauges well known in the art, in which change of resistance occurs in the gauge as a result of strain being applied to the gauge. (A detailed description of strain gages and application thereof to a Wheatstone bridge is found in Process Instruments and Control Handbook, McGraw- Hill, 1957, pages 340.) Accordingly, the difference in potential across the output terminals A and C becomes a measure of the difference of the strains applied by way of rods 80 and 82. Thus the amount of strain applied to strain gauge S or the resistance thereof is proportional to the pressure difference indicated by pressure differentiating device 44. The strain applied to strain gauge R or the resistance thereof is proportional to the pressure difference indicated by pressure differentiating device 42. In accordance with the invention, the basic magnitudes of resistances S and R are such that the ratio of resistance S to resistance R is inversely proportional to the ratio of distance d2 to distance d1. Accordingly, with no flame present in the furnace chamber the existing stack effect is cancelled out as indicated by a zero bridge output at 78. On the other hand if a flame is present in space H of the combustion chamber the pressure differentiating device 42 will cause a strain to be applied to gauge R which strain is greater than the strain applied by pressure differentiating device 44 to gauge S. This difference will then be indicative of a flame present in the furnace, as indicated by voltage meter 78.

In view of the above it will be appreciated that the disclosed apparatus and method permits a more precise determination of'the absence or'presence of flame in the furnace, by virtue of the fact that it greatly reduces or eliminates the influence of the stack effect, other than that caused by the presence of the flame itself.

While I have illustrated and described several preferred embodiments of my invention, it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

I claim:

1. In a furnace for burning fuel suspended in air and provided with means to receive both fuel and combustion air in a fuel receiving zone and to burn said fuel in a fuel burning zone, said furnace having water-cooled walls for the generation of steam and having a furnace outlet remote from said fuel receiving zone to discharge the gaseous products of combustion; the combination of at least lower, intermediate and upper openings provided in the water-cooled wall of said furnace and mutually spaced in the gas flow sense; a large distance separating said intermediate opening from a first of said remaining openings; a short distance separating said intermediate opening from a second of said remaining openings; said large distance traversing said fuel burning zone to a greater extent than said short distance; means for obtaining through said openings impulses of the static pressure existing in said furnace at said locations; means for determining a first difference between the furnace pressures at said intermediate and first openings; means for determining a second difference between the furnace pres sures at said intermediate and second openings; means for correcting said first and second pressure differences inversely as the ratio of said large distance to said short distance; means for balancing said corrected first pressure difference against said corrected second pressure difference, and means for indicating the result of said balancing; whereby a balanced condition thereof is indicative of lack of flame in said fuel burning zone.

2. The apparatus as defined in claim 1 wherein said means for correcting said first and second pressure differences comprises a four arm Wheatstone bridge circuit having a first variable resistance applied to one pair of said arms and a second variable resistance applied to the other pair of said arms; said first and said second resistances being inversely proportional to said first and said second distances respectively; and means for indicating the output of said Wheastone bridge circuit whereby a balanced output condition of said Wheatstone bridge is indicative of lack of flame in said fuel burning zone.

3. In a furnace for burning fuel suspended in air and provided with means to receive both fuel and combustion air in a fuel receiving zone and to burn said fuel in a fuel burning zone, said furnace having water-cooled walls for the generation of steam and having a'furnace outlet remote from said fuel receiving zone to discharge the gaseous products of combustion; the combination of at least lower, intermediate and upper openings provided in the water-cooled wall of said furnace and mutually spaced in the gas flow sense; a large distance separating said intermediate opening from a first of said remaining openings; a short distance separating said intermediate opening from a second of said remaining openings; said large distance traversing said fuel burning zone to a greater extent than said short distance; means for obtaining through said openings impulses of the static pressure existing in said furnace at said locations; means for determining a first difference between the furnace pressures at said intermediate and first openings; means for determining a second difference between the furnace pressures at said intermediate and second openings; means for applying a first correction factor to said first pressure difference, and a second correction factor to said second pressure difference, the ratio of said first to said second correction factor being proportional to the ratio of said small to said large distance; means for balancing said corrected second pressure difference against said corrected first pressure difference; whereby a balanced condition will be indicative of lack of flame in said fuel burning zone.

4. The apparatus as defined in claim 3 wherein said means for applying a first and a second correction factor to said first and second pressure differences comprises a four arm Wheatstone bridge circuit having a first variable resistance applied to one pair of said arms and a second variable resistance applied to the other pair of said arms; said first and said second resistances being inversely proportionai to said first and said second distances respectively; means for indicating the output of said Wheatstone bridge circuit whereby a balanced output condition of said Wheatstone bridge is indicative of lack of flame in said fuel burning zone.

5. In a furnace for burning fuel suspended in air and provided with means to receive both fuel and combustion air in a fuel receiving zone and to burn said fuel in a fuel burning zone, said furnace having water-cooled walls for the generation of steam and having a furnace outlet remote from said fuel receiving zone to discharge the gaseous products of combustion; the combination of at least lower, intermediate and upper openings provided in the water-cooled wall of said furnace and mutually spaced in the gas flow sense; a large distance separating said intermediate opening from said lower openings; 21 short distance separating said intermediate opening from said upper openings; said large distance traversing said fuel burning zone to a greater extent than said short distance; means for obtaining through said openings impulses of the static pressure existing in said furnace at said locations; means for determining a first difference between the furnace pressures at said intermediate and upper openings; means for determining a second difference between the furnace pressures at said intermediate and lower openings; means for applying a first correction factor to said first pressure difference, and a second correction factor to said second pressure difference, the ratio of said first to said second correction factor being proportional to the ratio of said small to said large distance; means for subtracting said corrected second pressure difference from said corrected first pressure difference; whereby a zero result from said subtraction will be indicative of lack of flame in said fuel burning zone.

6. In a furnace for burning fuel suspended in air and provided with means to receive both fuel and combustion air in a fuel receiving zone and to burn said fuel in a fuel burning zone, said furnace having water-cooled walls for the generation of steam and having a furnace outlet remote from said fuel receiving zone to discharge the gaseous products of combustion; the combination of at least lower, intermediate and upper openings provided in the water-cooled Wall of said furnace and mutually spaced in the gas flow sense; a large distance separating said intermediate opening from said upper opening; a short distance separating said intermediate opening from said lower openings; said large distance traversing said fuel burning zone to a greater extent than said short distance; means for obtaining through said openings impulses of the static pressure existing in said furnace at said locations; means for determining a first difference between the furnace pressures at said intermediate and lower openings; means for determining a second difference between the furnace pressures at said intermediate and upper openings; means for applying a first correction factor to said first pressure difference, and a second correction factor to said second pressure difference, the ratio of said first to said second correction factor being proportional to the ratio of said small to said'large distance; means for subtracting said corrected second pressure difference from said corrected first pressure difference; whereby a zero result from said subtraction will be indicative of lack of flame in said fuel burning zone.

7. The method of determining absence or presence of a flame body in a vertical furnace chamber for burning fuel suspended in air as evidenced by a flame body within said chamber, said furnace having an upper zone and a Iower zone of moderate heat release intensity and an intermediate zone of a relatively high heat release intensity located between said upper and lower zones, said flame body being primarily situated within said high heat release zone, said method comprising the steps of:

(1) obtaining an indication of a first prevailing pressure difference across at least twofirst measuring points straddling at least a part of said high heat release zone, with said first points being vertically spaced apart a first distance;

(2) obtaining an indication of a second prevailing pressure difference across at least two second measuring points stradling at least a part of one of said moderate heat release zones, with said second points being vertically spaced about a second distance;

(3) and correcting said first and second pressure differentials inversely as the ratio of said first and second distances;

whereby the stack effect between said first and said second measuring points is cancelled out with absence of flame in said furnace chamber, and the difference of the stack effect between the said first and said second measuring points is prominently evident when a flame body is present in said furnace chamber.

References Cited by the Examiner UNITED STATES PATENTS 2,622,669 12/1952 'Caracristi et a1. 158-28 3,123,027 3/1964 Livingston -28 KENNETH w. SPRAGUE, Primary Examiner. 

1. IN A FURNACE FOR BURNING FUEL SUSPENDED IN AIR AND PROVIDED WITH MEANS TO RECEIVE BOTH FUEL AND COMBUSTION AIR IN A FUEL RECEIVING ZONE AND TO BURN SAID FUEL IN A FUEL BURNING ZONE, SAID FURNACE HAVING WATER-COOLED WALLS FOR THE GENERATION OF STEAM AND HAVING A FURNACE OUTLET REMOTE FROM SAID FUEL RECEIVING ZONE TO DISCHARGE THE GASEOUS PRODUCTS OF COMBUSTION; THE COMBINATION OF AT LEAST LOWER, INTERMEDIATE AND UPPER OPENINGS PROVIDED IN THE WATER-COOLED WALL OF SAID FURNACE AND MUTUALLY SPACED IN THE GAS FLOW SENSE; A LARGE DISTANCE SEPARATING SAID INTERMEDIATE OPENING FROM A FIREST OF SAID REMAINING OPENINGS; A SHORT DISTANCE SEPARATING SAID INTERMEDIATE OPENING FROM A SECOND OF SAID REMAINING OPENINGS; SAID LARGE DISTANCE TRAVERSING SAID FUEL BURNING ZONE TO A GREATER EXTENT THAN SAID SHORT DISTANCE; MEANS FOR OBTAINING THROUGH SAID OPENINGS IMPULSES OF THE STATIC PRESSURE EXISTING IN SAID FURNACE AT SAID LOCATIONS; MEANS FOR DETERMINING A FRIST DIFFERENCE BETWEEN THE FURNACE PRESSURES AT SAID INTERMEDIATE AND FIRST OPENINGS; MEANS FOR DETERMINING A SECOND DIFFERENCE BETWEEN THE FURNACE PRESSURES AT SAID INTERMEDIATE AND SECOND OPENINGS; MEANS IN CORRECTING SAID FIRST AND SECOND PRESSURE DIFFERENCES INVERSELY AS THE RATIO OF SAID LARGE DISTANCE TO SAID SHORT DISTANCE; MEANS FOR BALANCING SAID CORRECTED FIRST PRESSURE DIFFFERENCE AGAINST SAID CORRECTED SECOND PRESSURE DIFFERENCE, AND MEANS FOR INDICATING THE RESULT OF SAID BALANCING; WHEREBY A BALANCED CONDITION THEREOF IS INDICATIVE OF LACK OF FLAME IN SAID FUEL BURNING ZONE. 